Emily Oster isn't a baby doctor. She's an economist and a mom who wanted to know more about all those rules handed down to women after the pregnancy stick goes pink.

Only two cups of coffee a day! No alcohol. Beware deli meats.

Being pregnant, she said, felt a lot like being a child, so she decided to take a deep dive into research covering everything from wine and weight gain to prenatal testing and epidurals. What she found was some of the mainstays of pregnancy advice are based on inconclusive or downright faulty science.

To this data-cruncher, an associate professor in the University of Chicago's business school, those magical nine months became a question of correlation and causation.

Some of her conclusions? Weight gain during pregnancy is less important than a woman's starting weight and not gaining enough may be more harmful. Light drinking is fine (up to two glasses of wine a week in the first trimester and up to a glass a day in the second and third trimesters). And much of the evidence supports having three to four cups of coffee daily, which made Oster very, very happy.

There's more, of course, and not all of it runs counter to standard medical advice. And she happily reports in "Expecting Better," her book corralling all the research for other women to share, that her 2-year-old daughter, Penelope, is healthy and happy.

The book, from Penguin Press, is out this week. A conversation with Oster:

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AP: Have you written the "Freakonomics" of pregnancy?

Oster: I think it's right that it feels a little bit like 'Freakonomics' because Steve (Levitt) and I are both economists, but the goal here was really to write down an approach that was right for me. The approach being thinking carefully through all of these decisions, getting the best data that you can and then structuring the decision in a way that takes into account your personal preferences, tolerance for risk and all the kinds of things that we should be thinking about every day.

AP: Do you anticipate blowback from women and doctors because you're an economist and not a medical professional who helps manage pregnancies?

Oster: For sure but I certainly do not envision women reading this book and saying, 'Oh, like, I can deliver my own baby now, right?' I think that there's a real sense in which pregnancy should be something that you do with your doctor, but I think that for a lot of women the time you have with your doctors is limited and it can be difficult to get all of the answers to your questions.

AP: Are most pregnant women ill-informed? Are doctors and other pregnancy professionals lax in keeping up to date on research that might lead to more specific recommendations?

Oster: I think we see sometimes where practice lags behind recommendations. Not all practitioners, obviously. As an example, in the case of prenatal testing, even though more recent recommendations don't favor the 35-year-old cutoff as much, that's still a highly practiced thing, so I think there's a sense in which there is some slow creep of knowledge.

I actually think pregnant women are really well-informed but I think that there's a tremendous amount of confusing and conflicting information out there. You could read every pregnancy book and every pregnancy website and come away thinking on some topics I have no idea what the real facts are.

AP: Isn't that what the American Congress of Obstetricians and Gynecologists is for? They have committees to vet research and keep up to date.

Oster: Yeah, it is, and actually in a lot of cases I found that women would do quite well to read the ACOG opinions. There were a few cases where I thought perhaps they were overly cautious but actually there's a lot of settings in which I think that would be a great place to start. There are certainly times in which practice hasn't really caught up to those opinions.

A lot of the choices that women need to make in pregnancy, it's sort of not possible for ACOG to tell them the right answer. For example, if you think about prenatal testing you're thinking about a case in which you're trading off more information about the baby for some small risk of miscarriage. Ultimately that needs to be combined with women's own ideas about how they feel about a miscarriage versus how they feel about a developmentally delayed child and that's not something a recommendation can tell you. That's something you need to learn to think through on your own.

AP: That leads me to the vices, including alcohol. You and ACOG differ on that one. ACOG recommends no alcohol.

Oster: I think we can all agree that heavy drinking and binge drinking, even occasionally, is very dangerous, and I certainly say that in the book. What I found is there are a large number of quite good studies with a lot of women that show having an occasional glass of wine does not seem to pose a problem, that children of pregnant women who drink occasionally have similar or in some cases even better outcomes than children of women who abstain. This is a very personal choice. In some other countries the recommendations are it's OK.

AP: When in this country did pregnancy become this exercise in self-denial? Are women needlessly suffering?

Oster: I think sometimes. I think we've moved this way over time and in some ways it's very good, thinking through pregnancy and parenting in a thoughtful and careful way. I think that's great. But I think there is, sometimes, this kind of shaming aspect to pregnancy. That's maybe not so productive.

AP: The editors at Parents.com have already called some of your recommendations flat-out dangerous to pregnant women, particularly your views on alcohol and caffeine consumption.

Oster: Many of the OBs that I have spoken to and many of the women who I have talked to about the recommendations from their doctors have told me that the doctors say, 'Yeah, it's fine to have a couple glasses of wine.' This is a conversation which will continue to evolve.

AP: What were some of the surprises when you started digging into the research?

Oster: One thing that came up that I found quite surprising is that a number of women that I knew who have been pregnant were put on bed rest. When I started looking into that more I found the evidence doesn't really support any benefit from bed rest in terms of preventing preterm labor. I think that lately doctors have started moving away from that pretty extensively. It has some negative impact, particularly around issues of muscle atrophy and other medical reasons.

AP: Should women trust their doctors?

Oster: Absolutely. But women have a responsibility to learn things about this process for themselves so they can actively participate in this conversation with their doctors.

AP: What are your top five fallacies about pregnancy?

Oster: One is that much of the evidence suggested an occasional drink is OK. Bed rest is not a great idea. Gaining too much weight may in fact be less risky than gaining too little weight. Sushi is OK. And coffee in moderation is fine.

And in terms of toxoplasmosis, which is a parasitic infection that can cause birth defects, when I looked at the data on this, there's actually no evidence that women who clean the cat litter box or have cats are more likely to get this, but I do see some links between doing a lot of outdoor gardening and having this infection. There are all kinds of animals that might poop in your garden. Not just cats.

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